1. Field of the Invention
The present invention relates to a lamp ballast circuit for driving multiple parallel lamps, and more particularly to a ballast circuit including a circuit for detection of when a lamp is inserted.
2. Related Art
There are several ways to drive four (for example) fluorescent lamps with an electronic ballast, including series configuration, parallel configuration and combined series and parallel configuration. But driving the four lamps in parallel has the advantage of lower voltage stress on the ballast output stage components, the wiring and the fixture sockets, as compared to the others. In addition, the resonant inductors and capacitors associated with the lamps will be less sensitive to component tolerances because running lamp voltage is lower. Further, even when one or more lamps is removed, the others can continue to run. For these reasons, the parallel configuration is more popular nowadays.
An excellent fluorescent lamp driver IC is the IR2167 manufactured by the International Rectifier Corporation. The IR2167 allows setting the various parameters such as preheat time and frequency, ignition ramp characteristics, running frequency and power through external programmable components. And comprehensive protection features of the IR2167 protect the overall circuitry from failure conditions such as lamp strike failures, lamp failures, low DC BUS and thermal overload. Also, the IR2167 controls its PFC circuitry with the critical conduction mode, which provides high power factor, low THD and DC Bus regulation. Thus, the IR2167 will be a suitable example, although not the only possible example, of a chip for use with the circuits to be described herein.